Centrifugal impeller and pump apparatus

ABSTRACT

The centrifugal impeller includes a plurality of blades ( 3 ), a plurality of fluid paths (P) for delivering a fluid from an impeller inlet ( 1 ) to an impeller outlet ( 2 ), and a shroud ( 4 ) and a hub ( 5 ) for forming the fluid paths (P). Each of the fluid paths (P) is formed between adjacent two of the blades ( 3 ). A curved line (L 3 ) of the shroud ( 4 ) curves so as to project toward the hub ( 5 ) in a region from a blade inlet (A) to a predetermined position (C) of the blade ( 3 ), and the curved line (L 3 ) curves so as to project toward the opposite side of the hub ( 5 ) in a region from the predetermined position (C) to a blade outlet (B).

TECHNICAL FIELD

The present invention relates to a centrifugal impeller and a pumpapparatus, and more particularly to a centrifugal impeller used in acentrifugal pump such as a volute pump to pressurize a fluid byimparting kinetic energy to the fluid due to a centrifugal force, and apump apparatus having such a centrifugal impeller.

BACKGROUND ART

In a centrifugal impeller shown in FIGS. 1A and 1B, an inlet width B₁and an outlet width B₂ of a blade 110, an inlet diameter D₀ and anoutlet diameter D₂ of the centrifugal impeller, and an inlet angle β₁and an outlet angle β₂ of the blade 110 are designed so as to satisfy arequired flow rate and a required pump head. In the conventionalcentrifugal impeller, it is desirable to change the width of the blade110 gradually from the inlet width B₁ to the outlet width B₂, and it isalso desirable to change the angle of the blade 110 gradually from theinlet angle β₁ to the outlet angle β₂.

FIGS. 2A and 2B are meridional-plane cross-sectional views showing aconventional centrifugal impeller designed as stated above. As shown inFIGS. 2A and 2B, the centrifugal impeller has a plurality of blades 110disposed between a shroud 120 and a hub 130 (only one blade is shown inFIGS. 2A and 2B). The blades 110 are arranged at angularly equalintervals in a circumferential direction of the centrifugal impeller. Afluid path 140 is formed by adjacent two of the blades 110, the shroud120, and the hub 130 so that a fluid flows through the fluid path 140.In the conventional centrifugal impeller shown in FIG. 2A, the shroud120 curves entirely so as to project toward the hub 130 to form a curvedline L₁. In the conventional centrifugal impeller shown in FIG. 2B, theshroud 120 is inclined straightly toward the hub 130 to form a straightline L₂.

However, as shown in FIGS. 2A and 2B, if the curved line L₁ or thestraight line L₂ is formed at the shroud 120, a meridional length of thefluid path 140 becomes long and a width of the whole fluid path 140 inthe meridional-plane cross-section becomes small in the case of thecentrifugal impeller of a small flow rate and a high pump head, i.e. asmall specific speed (Ns). Consequently, a relative velocity of thefluid flowing through the fluid path 140 becomes large, and hence afriction loss in the fluid path 140 is increased, thus lowering animpeller performance.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above drawbacks. Itis therefore an object of the present invention to provide a centrifugalimpeller which can reduce an internal loss in a fluid path to exhibit anexcellent performance even if the centrifugal impeller has a smallspecific speed, and to provide a pump apparatus having such acentrifugal impeller.

In order to achieve the above object, according to one aspect of thepresent invention, there is provided a centrifugal impeller comprising:a plurality of blades disposed between an impeller inlet and an impelleroutlet; a plurality of fluid paths for delivering a fluid from theimpeller inlet to the impeller outlet with the rotation of thecentrifugal impeller, each of the fluid paths being formed betweenadjacent two of the blades; and a shroud and a hub for forming the fluidpaths; wherein in a meridional-plane cross-section of the centrifugalimpeller, a curved line of the shroud, which forms the fluid path,curves so as to project toward the hub in a region from a blade inlet toa predetermined position of the blade, and the curved line curves so asto project toward the opposite side of the hub in a region from thepredetermined position of the blade to a blade outlet.

In a preferred aspect of the present invention, the predeterminedposition is located near a center of the blade in a meridional plane.

According to the present invention, compared to the conventionalcentrifugal impeller, the relative velocity of the fluid flowing throughthe fluid path can be reduced. Specifically, in the conventionalcentrifugal impeller, a meridional velocity of the fluid flowing throughthe fluid path is substantially constant in a region from the bladeinlet to the blade outlet. In contrast thereto, in the centrifugalimpeller according to the present invention, the fluid path can bewidened in a region from the blade inlet to the predetermined position,e.g. a position near the center of the blade, and hence a meridionalvelocity of the fluid flowing through the fluid path can be reducedgreatly. Therefore, the internal loss in the fluid path can be reduced,and hence the excellent impeller performance can be obtained even if thecentrifugal impeller has a small specific speed.

In a preferred aspect of the present invention, stream lines formed at aside of the hub and a side of the shroud correspond to each other whenviewed in an axial direction of the centrifugal impeller.

In a preferred aspect of the present invention, a distance betweenadjacent two of the blades is gradually increased from the blade inletto the predetermined position of the blade, and is decreased from thepredetermined position of the blade toward the blade outlet.

According to the present invention, because a region where a fluidvelocity is reduced can be extended to the downstream side of the fluidpath compared to the conventional centrifugal impeller, a frictionbetween the fluid and the fluid path can be reduced. Further, becausenon-uniformity of velocity distribution at the blade outlet can beimproved, a shearing force produced in the fluid can be reduced, andhence a loss at the downstream region of the fluid path can be reduced.The non-uniformity of velocity distribution herein refers tonon-uniformity of a fluid velocity in a direction perpendicular to aflowing direction of the fluid.

According to another aspect of the present invention, there is provideda centrifugal impeller comprising: a plurality of blades disposedbetween an impeller inlet and an impeller outlet; a plurality of fluidpaths for delivering a fluid from the impeller inlet to the impelleroutlet with the rotation of the centrifugal impeller, each of the fluidpaths being formed between adjacent two of the blades; and a shroud anda hub for forming the fluid paths; wherein a distance between adjacenttwo of the blades is gradually increased from a blade inlet to apredetermined position of the blade, and is decreased from thepredetermined position of the blade toward a blade outlet.

In a preferred aspect of the present invention, the predeterminedposition of the blade is located near a center of the blade in ameridional plane.

In a preferred aspect of the present invention, stream lines formed at aside of the hub and a side of the shroud correspond to each other whenviewed in an axial direction of the centrifugal impeller.

According to another aspect of the present invention, there is provideda pump apparatus comprising: the centrifugal impeller; a casing forhousing the centrifugal impeller; and a rotatable main shaft to whichthe centrifugal impeller is attached.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a cross-sectional view showing a general centrifugalimpeller;

FIG. 1B is a meridional-plane cross-sectional view showing the generalcentrifugal impeller;

FIG. 2A is a meridional-plane cross-sectional view showing aconventional centrifugal impeller whose shroud curves so as to projecttoward a hub;

FIG. 2B is a meridional-plane cross-sectional view showing aconventional centrifugal impeller whose shroud is inclined straightlytoward a hub;

FIG. 3 is a meridional-plane cross-sectional view showing a centrifugalimpeller according to a first embodiment of the present invention;

FIG. 4 is a cross-sectional view of the centrifugal impeller shown inFIG. 3;

FIG. 5A is a graph comparing a relative velocity of a fluid of thecentrifugal impeller according to the present invention to that of theconventional centrifugal impeller;

FIG. 5B is a graph comparing characteristics of the centrifugal impelleraccording to the present invention to those of the conventionalcentrifugal impeller;

FIGS. 6A through 6E are views showing examples of designs of thecentrifugal impeller according to the present invention, FIG. 6A showingthe centrifugal impeller having a specific speed of 120, FIG. 6B showingthe centrifugal impeller having a specific speed of 140, FIG. 6C showingthe centrifugal impeller having a specific speed of 200, FIG. 6D showingthe centrifugal impeller having a specific speed of 240, and FIG. 6Eshowing the centrifugal impeller having a specific speed of 280; and

FIG. 7 is a vertical cross-sectional view showing an example of a pumpapparatus having the centrifugal impeller according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

A centrifugal impeller according to an embodiment of the presentinvention will be described below with reference to the drawings. FIG. 3is a meridional-plane cross-sectional view showing a centrifugalimpeller according to a first embodiment of the present invention. FIG.4 is a cross-sectional view of the centrifugal impeller shown in FIG. 3.

As shown in FIGS. 3 and 4, a centrifugal impeller comprises a pluralityof blades 3 (only adjacent two of the blades 3 are shown in FIG. 4), ashroud (tip) 4, and a hub 5. The blades 3 are disposed between theshroud 4 and the hub 5 along an axial direction of the centrifugalimpeller and also disposed between an impeller inlet 1 positioned at acentral side of the centrifugal impeller and an impeller outlet 2positioned at a circumferential side of the centrifugal impeller. Theblades 3 are arranged at angularly equal intervals in a circumferentialdirection of the centrifugal impeller and extend outwardly spirally. Aplurality of fluid paths P are formed between the adjacent blades 3 sothat a fluid is delivered through the fluid paths P from the impellerinlet 1 to the impeller outlet 2 with the rotation of the centrifugalimpeller. Specifically, spaces surrounded by the adjacent blades 3, theshroud 4, and the hub 5 constitute the fluid paths P, respectively. Onlyone of the fluid paths P is shown in FIGS. 3 and 4. As shown in FIG. 4,the centrifugal impeller of this embodiment comprises a two-dimensionalimpeller whose stream lines at a side of the hub 5 and a side of theshroud 4 correspond to each other when viewed in the axial direction ofthe centrifugal impeller. Specifically, the respective blades 3 extendfrom the hub 5 to the shroud 4 in a direction perpendicular to a surfaceof the hub 5.

In the meridional-plane cross-section of the centrifugal impeller shownin FIG. 3, a curved line L₃ of the shroud 4, which forms the fluid pathP, curves so as to project toward the hub 5 in a region of a meridionallength M₁ from a blade inlet A to a position C near the center of theblade 3 in a meridional plane (hereinafter referred to as a near-centerposition C) so that the fluid path P is widened from the blade inlet Ato the near-center position C. The curved line L₃ also curves so as toproject toward the opposite side of the hub 5 in a region of ameridional length M₂ from the near-center position C to a blade outlet Bso that the fluid path P is widened at a region downstream of thenear-center position C and narrowed sharply in the vicinity of the bladeoutlet B.

With this structure, since the fluid path P can be widened in the regionfrom the blade inlet A to the near-center position C, a meridionalvelocity of the fluid flowing through the fluid path P can be reducedgreatly, and hence a relative velocity of the fluid in the fluid path Pcan be reduced compared to the conventional centrifugal impeller.Further, since the fluid path P is narrowed in the vicinity of the bladeoutlet B, a flow rate of the fluid discharged from the centrifugalimpeller is reduced, and hence a desired flow rate can be obtained. FIG.5A is a graph comparing the relative velocity of the fluid of thecentrifugal impeller according to the present invention to that of theconventional centrifugal impeller, and FIG. 5B is a graph comparingcharacteristics of the centrifugal impeller according to the presentinvention to those of the conventional centrifugal impeller. In FIGS. 5Aand 5B, solid lines represent the present invention, and broken linesrepresent the conventional.

As shown in FIG. 5A, according to the centrifugal impeller of thepresent invention, the relative velocity of the fluid can be reduced ina region from the blade inlet A to the blade outlet B, compared to theconventional centrifugal impeller. Therefore, since an internal loss inthe fluid path P can be reduced, an excellent impeller performance canbe obtained even if the impeller has a small specific speed. Further, asshown in FIG. 5A, in the centrifugal impeller of the present invention,since the relative velocity of the fluid at the blade outlet B does notchange compared to the conventional centrifugal impeller, Euler headalso does not change, and hence a shaft power is not increased and apump efficiency is increased, as shown in FIG. 5B. Euler head is definedas a theoretical head given by Euler's equation.

In the cross-sectional view shown in FIG. 4, a distance between theadjacent blades 3 is set such that a distance a₁ at the blade inlet A issmaller than a distance a₂ at the near-center position C (a₁<a₂) and adistance a₃ at the blade outlet B is smaller than the distance a₂(a₃<a₂), so that the distance between the adjacent blades 3 is graduallyincreased from the blade inlet A toward the near-center position C, andis decreased from the near-center position C toward the blade outlet B.Since the distance a₁ at the blade inlet A and the distance a₂ at thenear-center position C are large, a region where the fluid velocity isreduced can be extended to a downstream side of the fluid path Pcompared to the conventional centrifugal impeller. Therefore, thecentrifugal impeller of the present invention can reduce a fluidfriction between the fluid and the fluid path P compared to theconventional centrifugal impeller. Further, since the distance a₃ issmaller than the distance a₂, non-uniformity of velocity distribution atthe blade outlet B can be improved. Accordingly, a shearing forceproduced in the fluid can be reduced, and hence a loss at the downstreamregion of the fluid path P can be reduced.

The shape of the centrifugal impeller of the present invention can bereproduced using a three-dimensional inverse design method. Thethree-dimensional inverse design method is a design technique in which ablade loading distribution is specified and a blade geometry which willrealize the specified blade loading distribution is determined bynumeral calculation. Theory of the three-dimensional inverse designmethod is described in detail in the following literature: Zangeneh, M.,1991, “A Compressible Three-Dimensional Design Method for Radial andMixed Flow Turbomachinery Blades”, Int. J. Numerical Methods in Fluids,Vol. 13, pp. 599-624. FIGS. 6A through 6E are views showing examples ofdesigns of the centrifugal impeller according to the present inventionand showing modifications of the centrifugal impeller whose specificspeed increases gradually from FIG. 6A to FIG. 6E. FIG. 6A shows thecentrifugal impeller having a specific speed of 120, FIG. 6B shows thecentrifugal impeller having a specific speed of 140, FIG. 6C shows thecentrifugal impeller having a specific speed of 200, FIG. 6D shows thecentrifugal impeller having a specific speed of 240, and FIG. 6E showsthe centrifugal impeller having a specific speed of 280.

In the centrifugal impeller, there are a friction loss due to a fluidfriction between the fluid and an inner surface of the fluid path, and amixing loss due to the non-uniformity of velocity distribution. Ingeneral, the lower the specific speed is, the higher the friction lossis. According to the present invention, since the relative velocity ofthe fluid flowing through the fluid path can be small, the friction losscan be reduced. Therefore, the centrifugal impeller according to thepresent invention is effective in an impeller having a small specificspeed, and it is possible to construct a pump apparatus having anexcellent pump performance by using the centrifugal impeller of thepresent invention attached to a rotatable main shaft.

FIG. 7 is a vertical cross-sectional view showing an example of a pumpapparatus having the centrifugal impeller according to the presentinvention. The pump apparatus shown in FIG. 7 is only an example of anapplication of the present invention, and the centrifugal impeller ofthe present invention can be applied to all types of pump apparatuses.

The pump apparatus shown in FIG. 7 comprises a motor section 12 having amotor 10, a pump section 16 in which the centrifugal impeller 14according to the present invention is incorporated. A main shaft 18extends from the motor section 12 to the pump section 16, and thecentrifugal impeller 14 is fixed to a lower end portion of the mainshaft 18. With this structure, a driving force generated by the motor 10of the motor section 12 is transmitted to the centrifugal impeller 14 ofthe pump section 16 through the main shaft 18, thereby rotating thecentrifugal impeller 14 together with the main shaft 18.

The pump section 16 comprises a casing 24 having a suction port 20 and adischarge port 22, and an intermediate casing 25 housed in the casing24. The centrifugal impeller 14 is housed in the intermediate casing 25in such a state that an impeller inlet 1 of the centrifugal impeller 14faces downwardly. The intermediate casing 25 has an opening portion 25 aat a lower portion thereof for allowing an interior of the intermediatecasing 25 to communicate with an interior of the casing 24. The suctionport 20 is located at one side portion of the casing 24 and communicateswith the interior of the casing 24, and the discharge port 22 is locatedat the opposite side portion of the casing 24 and communicates with theinterior of the intermediate casing 25. A casing cover 26 is providedbetween the intermediate casing 25 and the motor section 12 to cover anopening of the intermediate casing 25. A mechanical seal 28 is disposedat a central portion of the casing cover 26 for thereby preventing apressurized fluid in the pump section 16 from entering the motor section12.

In the pump apparatus having such a structure, the driving force of themotor 10 is transmitted to the centrifugal impeller 14 fixed to thelower end portion of the main shaft 18, and kinetic energy is impartedto the fluid (liquid) in the casing 24 by the rotation of thecentrifugal impeller 14. Therefore, when the centrifugal impeller 14 isrotated by energizing the motor 10, the fluid is sucked from the suctionport 20 into the interior of the casing 24, and is pressurized and thendischarged from the discharge port 22.

While the present invention has been described with reference to anembodiment thereof, many modifications and variations may be made in thepresent invention without departing from the spirit and scope of thepresent invention.

As described above, according to the present invention, compared to theconventional centrifugal impeller, the relative velocity of the fluidflowing through the fluid path can be reduced. Therefore, the internalloss in the fluid path can be reduced, and hence an excellent impellerperformance can be obtained even if the centrifugal impeller has a smallspecific speed.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a centrifugal impeller and a pumpapparatus, and more particularly to a centrifugal impeller used in acentrifugal pump such as a volute pump to pressurize a fluid byimparting kinetic energy to the fluid due to a centrifugal force, and apump apparatus having such a centrifugal impeller.

1. A centrifugal impeller comprising: a plurality of blades disposed between an impeller inlet and an impeller outlet; a plurality of fluid paths for delivering a fluid from said impeller inlet to said impeller outlet with the rotation of said centrifugal impeller, each of said fluid paths being formed between adjacent two of said blades; and a shroud and a hub for forming said fluid paths; wherein in a meridional-plane cross-section of said centrifugal impeller, a curved line of said shroud, which forms said fluid path, curves so as to project toward said hub in a region from a blade inlet to a predetermined position of said blade so that said fluid path is widened from said blade inlet to aid predetermined position, and said curved line curves so as to project toward the opposite side of said hub in a region from said predetermined position of said blade to a blade outlet so that said fluid path is widened in a region downstream of said predetermined position and narrowed in the vicinity of said blade outlet.
 2. A centrifugal impeller according to claim 1, wherein said predetermined position of said blade is located near a center of said blade in a meridional plane.
 3. A centrifugal impeller according to claim 1 or 2, wherein stream lines formed at a side of said hub and a side of said shroud correspond to each other when viewed in an axial direction of said centrifugal impeller.
 4. A centrifugal impeller according to claim 1 or 2, wherein a distance between adjacent two of said blades is gradually increased from said blade inlet to said predetermined position of said blade, and is decreased from said predetermined position of said blade toward said blade outlet.
 5. A centrifugal impeller comprising: a plurality of blades disposed between an impeller inlet and an impeller outlet; a plurality of fluid paths for delivering a fluid from said impeller inlet to said impeller outlet with the rotation of said centrifugal impeller, each of said fluid paths being formed between adjacent two of said blades; and a shroud and a hub for forming said fluid paths; wherein a distance between adjacent two of said blades is gradually increased from a blade inlet to a predetermined position of said blade, and is decreased from said predetermined position of said blade toward a blade outlet.
 6. A centrifugal impeller according to claim 5, wherein said predetermined position of said blade is located near a center of said blade in a meridional plane.
 7. A centrifugal impeller according to claim 5 or 6, wherein stream lines formed at a side of said hub and a side of said shroud correspond to each other when viewed in an axial direction of said centrifugal impeller.
 8. A pump apparatus comprising: a centrifugal impeller according to claim 1, 2, 5 or 6 a casing for housing said centrifugal impeller; and a rotatable main shaft to which said centrifugal impeller is attached. 